Date:   Mon, 10 Dec 2018 10:31:57 +0000
From:   Schrempf Frieder <frieder.schrempf@...tron.de>
To:     Boris Brezillon <boris.brezillon@...tlin.com>,
        Yogesh Narayan Gaur <yogeshnarayan.gaur@....com>
CC:     "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "marek.vasut@...il.com" <marek.vasut@...il.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "robh@...nel.org" <robh@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "computersforpeace@...il.com" <computersforpeace@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 1/5] spi: spi-mem: Add driver for NXP FlexSPI
 controller

Hi Yogesh, Boris,

On 10.12.18 11:19, Boris Brezillon wrote:
> On Mon, 10 Dec 2018 09:41:51 +0000
> Yogesh Narayan Gaur <yogeshnarayan.gaur@....com> wrote:
> 
>>>> +/* Instead of busy looping invoke readl_poll_timeout functionality.
>>>> +*/ static int fspi_readl_poll_tout(struct nxp_fspi *f, void __iomem *base,
>>>> +				u32 mask, u32 delay_us,
>>>> +				u32 timeout_us, bool condition)
>>>> +{
>>>> +	u32 reg;
>>>> +
>>>> +	if (!f->devtype_data->little_endian)
>>>> +		mask = (u32)cpu_to_be32(mask);
>>>> +
>>>> +	if (condition)
>>>> +		return readl_poll_timeout(base, reg, (reg & mask),
>>>> +					  delay_us, timeout_us);
>>>> +	else
>>>> +		return readl_poll_timeout(base, reg, !(reg & mask),
>>>> +					  delay_us, timeout_us);
>>>
>>> I would rather use a local variable to store the condition:
>>>
>>> bool c = condition ? (reg & mask):!(reg & mask);
>>>    
>> With these type of usage getting below warning messages.
>>   
>> drivers/spi/spi-nxp-fspi.c: In function ‘fspi_readl_poll_tout.isra.10.constprop’:
>> drivers/spi/spi-nxp-fspi.c:446:21: warning: ‘reg’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>>    bool cn = c ? (reg & mask) : !(reg & mask);
>>
>> If assign value to reg = 0xffffffff then timeout is start getting hit for False case and if assign value 0 then start getting timeout hit for true case.
>>
>> I would rather not try to modify this function.
> 
> I agree. Let's keep this function readable even if this implies
> duplicating a few lines of code.

My bad. This doesn't work of course. We need to pass the actual 
expression containing reg to the readl_poll_timeout() macro. So forget 
about my comment.

> 
>>
>>> return readl_poll_timeout(base, reg, c, delay_us, timeout_us);
>>>    
>>>> +}
>>>> +
>>>> +/*
>>>> + * If the slave device content being changed by Write/Erase, need to
>>>> + * invalidate the AHB buffer. This can be achieved by doing the reset
>>>> + * of controller after setting MCR0[SWRESET] bit.
>>>> + */
>>>> +static inline void nxp_fspi_invalid(struct nxp_fspi *f) {
>>>> +	u32 reg;
>>>> +	int ret;
>>>> +
>>>> +	reg = fspi_readl(f, f->iobase + FSPI_MCR0);
>>>> +	fspi_writel(f, reg | FSPI_MCR0_SWRST, f->iobase + FSPI_MCR0);
>>>> +
>>>> +	/* w1c register, wait unit clear */
>>>> +	ret = fspi_readl_poll_tout(f, f->iobase + FSPI_MCR0,
>>>> +				   FSPI_MCR0_SWRST, 0, POLL_TOUT, false);
>>>> +	WARN_ON(ret);
>>>> +}
>>>> +
>>>> +static void nxp_fspi_prepare_lut(struct nxp_fspi *f,
>>>> +				 const struct spi_mem_op *op)
>>>> +{
>>>> +	void __iomem *base = f->iobase;
>>>> +	u32 lutval[4] = {};
>>>> +	int lutidx = 1, i;
>>>> +
>>>> +	/* cmd */
>>>> +	lutval[0] |= LUT_DEF(0, LUT_CMD, LUT_PAD(op->cmd.buswidth),
>>>> +			     op->cmd.opcode);
>>>> +
>>>> +	/* addr bus width */
>>>> +	if (op->addr.nbytes) {
>>>> +		u32 addrlen = 0;
>>>> +
>>>> +		switch (op->addr.nbytes) {
>>>> +		case 1:
>>>> +			addrlen = ADDR8BIT;
>>>> +			break;
>>>> +		case 2:
>>>> +			addrlen = ADDR16BIT;
>>>> +			break;
>>>> +		case 3:
>>>> +			addrlen = ADDR24BIT;
>>>> +			break;
>>>> +		case 4:
>>>> +			addrlen = ADDR32BIT;
>>>> +			break;
>>>> +		default:
>>>> +			dev_err(f->dev, "In-correct address length\n");
>>>> +			return;
>>>> +		}
>>>
>>> You don't need to validate op->addr.nbytes here, this is already done in
>>> nxp_fspi_supports_op().
>>
>> Yes, I need to validate op->addr.nbytes else LUT would going to be programmed for 0 addrlen.
>> I have checked this on the target.
> 
> Also agree there. Some operations have 0 address bytes. We could also
> test addr.buswidth, but I'm fine with the addr.nbytes test too.

The "if (op->addr.nbytes)" is needed of course, but I think the default 
case in the switch statement (and for other reasons the whole switch 
statement) is not needed and rather a check for op->addr.nbytes > 4 
should be added to nxp_fspi_supports_op(). I wrongly assumed this check 
already exists in nxp_fspi_supports_op().

> 
>>>> +static void nxp_fspi_select_mem(struct nxp_fspi *f, struct spi_device
>>>> +*spi) {
>>>> +	unsigned long rate = spi->max_speed_hz;
>>>> +	int ret;
>>>> +	uint64_t size_kb;
>>>> +
>>>> +	/*
>>>> +	 * Return, if previously selected slave device is same as current
>>>> +	 * requested slave device.
>>>> +	 */
>>>> +	if (f->selected == spi->chip_select)
>>>> +		return;
>>>> +
>>>> +	/* Reset FLSHxxCR0 registers */
>>>> +	fspi_writel(f, 0, f->iobase + FSPI_FLSHA1CR0);
>>>> +	fspi_writel(f, 0, f->iobase + FSPI_FLSHA2CR0);
>>>> +	fspi_writel(f, 0, f->iobase + FSPI_FLSHB1CR0);
>>>> +	fspi_writel(f, 0, f->iobase + FSPI_FLSHB2CR0);
>>>> +
>>>> +	/* Assign controller memory mapped space as size, KBytes, of flash. */
>>>> +	size_kb = FSPI_FLSHXCR0_SZ(f->memmap_phy_size);
>>>    
>> Above description of this function, explains the reason for using memmap_phy_size.
>> This is not the arbitrary size, but the memory mapped size being assigned to the controller.
>>
>>> You are still using memory of arbitrary size (memmap_phy_size) for mapping the
>>> flash. Why not use the same approach as in the QSPI driver and just map
>>> ahb_buf_size until we implement the dirmap API?
>> The approach which being used in QSPI driver didn't work here, I have tried with that.
>> In QSPI driver, while preparing LUT we are assigning read/write address in the LUT preparation and have to for some unknown hack have to provide macro for LUT_MODE instead of LUT_ADDR.
>> But this thing didn't work for FlexSPI.
>> I discussed with HW IP owner and they suggested only to use LUT_ADDR for specifying the address length of the command i.e. 3-byte or 4-byte address command (NOR) or 1-2 byte address command for NAND.
> 
> Actually, we would have used a LUT_ADDR too if the QSPI IP was support
> ADDR instructions with a number of bytes < 3, but for some unknown
> reasons it does not work.
> 
>>
>> Thus, in LUT preparation we have assigned only the base address.
>> Now if I have assigned ahb_buf_size to FSPI_FLSHXXCR0 register then for read/write data beyond limit of ahb_buf_size offset I get data corruption.
> 
> Why would you do that? We have the ->adjust_op_size() exactly for this
> reason, so, if someone tries to do a spi_mem_op with data.nbytes >
> ahb_buf_size you should return an error.
> 
>>
>> Thus, for generic approach have assigned FSPI_FLSHXXCR0 equal to the memory mapped size to the controller. This would also not going to depend on the number of CS present on the target.
> 
> I kind of agree with Frieder on that one, I think it's preferable to
> limit the per-read-op size to ahb_buf_size and let the upper layer
> split the request in several sub-requests. On the controller side of
> things, you just have to have a mapping of ahb_buf_size per-CS. If you
> want to further optimize things, implement the dirmap hooks.
> 
>>
>>> You are already aligning the AHB reads for this in nxp_fspi_adjust_op_size().
>>>    
>> Yes, max read data size can be ahb_buf_size. Thus we need to check max read size with ahb_buf_size.
> 
> Well, it's never a bad thing to check it twice, just in case the
> spi-mem user is misusing the API.
> 
>>>> +static void nxp_fspi_fill_txfifo(struct nxp_fspi *f,
>>>> +				 const struct spi_mem_op *op)
>>>> +{
>>>> +	void __iomem *base = f->iobase;
>>>> +	int i, j, ret;
>>>> +	int size, tmp_size, wm_size;
>>>> +	u32 data = 0;
>>>> +	u32 *txbuf = (u32 *) op->data.buf.out;
>>>> +
>>>> +	/* clear the TX FIFO. */
>>>> +	fspi_writel(f, FSPI_IPTXFCR_CLR, base + FSPI_IPTXFCR);
>>>> +
>>>> +	/* Default value of water mark level is 8 bytes. */
>>>> +	wm_size = 8;
>>>> +	size = op->data.nbytes / wm_size;
>>>> +	for (i = 0; i < size; i++) {
>>>> +		/* Wait for TXFIFO empty */
>>>> +		ret = fspi_readl_poll_tout(f, f->iobase + FSPI_INTR,
>>>> +					   FSPI_INTR_IPTXWE, 0,
>>>> +					   POLL_TOUT, true);
>>>> +		WARN_ON(ret);
>>>> +
>>>> +		j = 0;
>>>> +		tmp_size = wm_size;
>>>> +		while (tmp_size > 0) {
>>>> +			data = 0;
>>>> +			memcpy(&data, txbuf, 4);
>>>> +			fspi_writel(f, data, base + FSPI_TFDR + j * 4);
>>>> +			tmp_size -= 4;
>>>> +			j++;
>>>> +			txbuf += 1;
>>>> +		}
>>>> +		fspi_writel(f, FSPI_INTR_IPTXWE, base + FSPI_INTR);
>>>> +	}
>>>> +
>>>> +	size = op->data.nbytes % wm_size;
>>>> +	if (size) {
>>>> +		/* Wait for TXFIFO empty */
>>>> +		ret = fspi_readl_poll_tout(f, f->iobase + FSPI_INTR,
>>>> +					   FSPI_INTR_IPTXWE, 0,
>>>> +					   POLL_TOUT, true);
>>>> +		WARN_ON(ret);
>>>> +
>>>> +		j = 0;
>>>> +		tmp_size = 0;
>>>> +		while (size > 0) {
>>>> +			data = 0;
>>>> +			tmp_size = (size < 4) ? size : 4;
>>>> +			memcpy(&data, txbuf, tmp_size);
>>>> +			fspi_writel(f, data, base + FSPI_TFDR + j * 4);
>>>> +			size -= tmp_size;
>>>> +			j++;
>>>> +			txbuf += 1;
>>>> +		}
>>>> +		fspi_writel(f, FSPI_INTR_IPTXWE, base + FSPI_INTR);
>>>> +	}
>>>
>>> All these nested loops to fill the TX buffer and also the ones below to read the
>>> RX buffer look much more complicated than they should really be. Can you try to
>>> make this more readable?
>> Yes
>>>
>>> Maybe something like this would work:
>>>
>>> for (i = 0; i < ALIGN_DOWN(op->data.nbytes, 8); i += 8) {
>>> 	/* Wait for TXFIFO empty */
>>> 	ret = fspi_readl_poll_tout(f, f->iobase + FSPI_INTR,
>>> 				   FSPI_INTR_IPTXWE, 0,
>>> 				   POLL_TOUT, true);
>>>
>>> 	fspi_writel(f, op->data.buf.out + i, base + FSPI_TFDR);
>>> 	fspi_writel(f, op->data.buf.out + i + 4, base + FSPI_TFDR + 4);
>>> 	fspi_writel(f, FSPI_INTR_IPTXWE, base + FSPI_INTR); }
>> With this above 2 lines we are hardcoding it for read/write with watermark size as 8 bytes.
>> Watermark size can be variable and depends on the value of IPRXFCR/IPTXFCR register with default value as 8 bytes
>> Thus, I would still prefer to use the internal for loop instead of 2 fspi_writel(...) for FSPI_TFDR and FSPI_TFDR + 4 register write commands.
> 
> Just like you're hardcoding wm_size to 8, so I don't see a difference
> here. And I indeed prefer Frieder's version.

Yes, as long as the watermark level is fixed, we don't need the inner loop.

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